Field of the Invention
The present inventions relate to at least one of an image processing apparatus, a data generation apparatus, an image processing method, and a data generation method capable of inputting image data in an image format with a wide dynamic range.
Description of the Related Art
Recently, imaging apparatuses capable of capturing an image with a wide dynamic range have been developed, and imaging apparatuses capable of outputting image data with log characteristics have been available. For example, Cineon-Log, created from characteristics of a film with a wide dynamic range, ACES-Log, corresponding to Academy Color Encoding Specification (ACES), and the like have been used in the motion picture industry.
On the other hand, display apparatuses are required to be capable of processing image data of various characteristics input from various imaging apparatuses. Some display apparatuses use a lookup table (LUT) to perform gradation conversion processing, color conversion processing, and the like on an image signal input from an imaging apparatus. Such display apparatuses can have a smaller implemented circuit size with a smaller number of grid points in the LUT. Thus, a grid point is not set for each possible gradation value of input image data. Instead, the number of grid points is set to be less than the possible number of gradation values of the image data. There is a method in which a LUT is generated in advance by calculating an output value obtained by conversion processing on the input value of image data for each grid point and output values corresponding to the input values of the image data between the grid points are calculated by interpolation. Generally, with a larger number of grid points, higher conversion accuracy is achieved, but a larger circuit size leads to a cost increase, especially in a three-dimensional LUT (3D-LUT). When the number of grid points is the same on all the three axes in the 3D-LUT, the total number of grid points is the third power of the number of grid points on a single axis.
Japanese Patent Application Laid-Open No. 2007-096797 discusses a technique of performing one-dimensional LUT (1D-LUT) conversion processing and 3D-LUT conversion processing in this order on data of each of red (R), green (G), and blue (B) colors. More specifically, the 1D-LUT conversion processing is performed on extracted common components of the conversion coefficients in the 3D-LUT conversion processing. Then, the 3D-LUT conversion processing is performed on coefficient components excluding the 1D-LUT conversion components that are common among data of each of R, G, and B colors.
Unfortunately, the method discussed in Japanese Patent Application Laid-Open No. 2007-096797 involves a large interpolation error when the LUT conversion processing is performed on image data with a wide dynamic range. More specifically, when the LUT conversion processing is performed on image data with a large dynamic range by using a LUT with the number of grid points that is the same as that of a LUT used when it is performed on image data with a narrow dynamic range, the interpolation in the LUT conversion processing results in a large error due to a large range between the adjacent grid points of the LUT.